Unbreak the build on architectures which still use GCC 4.2.1 as system
compiler. Guile attempts to redefine _Static_assert (in `lib/verify.h')
based on compiler support, but its overrides do not play nice with our
/usr/include/complex.h header file.

Simply do not include lib/verify.h' in libguile/numbers.c' to avoid
the problem. Be conservative and conditionally inhibit including this
header only when building with older versions of GCC (before 4.6.0).

While here, move INFO knob where it logically belongs in the Makefile
and add a couple of extra linefeeds to improve readability thereof.

Tested on: i386, powerpc, sparc64